Cervical length at 31-34 weeks of gestation: transvaginal vs. transperineal ultrasonographic approach

Objectives: To investigate the correlation between transperineal (TP) and transvaginal (TV) ultrasonography in the measurement of cervical length (CL) in the third trimester of pregnancy. Methods: In this prospective study, CL measurements were conducted in women between 31 and 34 weeks of gestation by both the TP and TV approaches. A comparison of the measurements was made between the two techniques. The Pearson correlation coefficient, the paired samples t-test and Bland-Altman plot were used. Results: In total, 240 women participated in the study. The CL was successfully measured transvaginally in all cases and transperineally in 229 (95.4%) of the cases. The mean TV CL was 32.8 +/- 8.2 mm and the mean TP CL was 32.5 +/- 8.1 mm. In the 229 cases with paired measurements, the Pearson correlation coefficient was 0.96.4. No significant differences in mean CL were identified between the two methods (t=1.805; P=0.072). In the Bland-Altman plot, the difference between the paired means was 0.26 mm and the 95% tolerance interval for any given paired observation (TV CL-TP CL) was -4.05 to 4.57 mm. Conclusion: The findings of this study suggest that at 31-34 weeks of gestation the cervix can be visualized adequately by both the TV and TP sonography in about 95% of cases. The TP CL measurements demonstrate a close correlation with the TV measurements. TP ultrasound is a feasible alternative, especially in cases where the use of the vaginal transducer should be minimized or is not acceptable by women.